Allied Telesis AT-GS950/10PS, AT-S110 manual Forwarding Delay Topology Changes, Step

Forwarding

Delay and

Topology

Changes

AT-GS950/10PS Switch Web Interface User’s Guide

.	Table 2. Valid Port Priority Values
		Step	Port
			Priority
		1	0
		2	16
		3	32
		4	48
		5	64
		6	80
		7	96
		8	112
		9	128
		10	144
		11	160
		12	176
		13	192
		14	208
		15	224
		16	240

If there is a change in the network topology due to a failure, removal, or addition of any active components, the active topology also changes. This may trigger a change in the state of some blocked ports. However, a change in a port state is not activated immediately.

It may take time for the root bridge to notify all bridges that a topology change has occurred, especially if it is a large network. A temporary data loop could occur if a topology change is made before all bridges have been notified and that could adversely impact network performance.

To forestall the formation of temporary data loops during topology changes, a port designated to change from blocking to forwarding passes through two additional states - listening and learning - before it begins to forward frames. The amount of time a port spends in these states is set by the forwarding delay value. This value states the amount of time that a port spends in the listening and learning states prior to changing to the forwarding state.

65